Summary It is proposed to develop an approach for constructing enzyme-based sensors for detecting biomolecules. The sensor is an enzyme modified by site-directed mutagenesis to create a binding site specific for a target biomolecule. A library of engineered enzyme sensors is constructed to serve as a repository of potential binders. The binding site is positioned in the immediate vicinity of the enzyme's active site such that the active site is allosterically affected by the binding of the biomolecule to the binding site. Binding is detected in a chemical reaction catalyzed by the enzyme using a chromogenic or fluorogenic substrate. Implementation will be straightforward and as simple as adding the biomolecule of interest, or a sample that contains it, to the enzyme sensor and observing the outcome of the reaction (i.e., color or fluorescence).